U.S. patent application number 09/933153 was filed with the patent office on 2002-03-14 for method and apparatus for image forming capable of performing an effective fixing process.
This patent application is currently assigned to RICOH CO., LTD.. Invention is credited to Ozaki, Koji, Tomita, Kunihiko.
Application Number | 20020031363 09/933153 |
Document ID | / |
Family ID | 27481549 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020031363 |
Kind Code |
A1 |
Tomita, Kunihiko ; et
al. |
March 14, 2002 |
Method and apparatus for image forming capable of performing an
effective fixing process
Abstract
A fixing apparatus includes a heater, an endless belt, a
pressure roller, and a heater controller. The heater has a line
shape orthogonal to a direction in which a recording sheet carrying
an unfixed toner image formed with toner in accordance with image
information is transferred. The endless belt is rotated with an
inner surface thereof sliding over a surface of the heater. The
pressure roller is arranged at a position opposite to the heater
relative to the endless belt and is held for rotation in contact
with the endless belt under pressure to form a nip therebetween.
The heater controller energizes the heater in accordance with the
image information. When the recording sheet is brought to the nip
with the unfixed toner image facing the endless belt, the pressure
roller applies pressure to the recording sheet against the endless
belt so that the unfixed toner image is fixed on the recording
sheet with heat as the recording sheet is transferred by movement
of the endless belt and the pressure roller.
Inventors: |
Tomita, Kunihiko;
(Kanagawa-ken, JP) ; Ozaki, Koji; (Tokyo,
JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
RICOH CO., LTD.
TOKYO
JP
|
Family ID: |
27481549 |
Appl. No.: |
09/933153 |
Filed: |
August 21, 2001 |
Current U.S.
Class: |
399/69 ; 219/216;
399/329 |
Current CPC
Class: |
G03G 2215/2016 20130101;
G03G 15/2064 20130101; G03G 2215/2022 20130101; G03G 2215/2032
20130101; G03G 2215/2035 20130101 |
Class at
Publication: |
399/69 ; 399/329;
219/216 |
International
Class: |
G03G 015/20 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 21, 2000 |
JP |
2000-249839 |
Nov 30, 2000 |
JP |
2000-365159 |
Sep 11, 2000 |
JP |
2000-274850 |
May 30, 2001 |
JP |
2001-163025 |
Claims
What is claimed as new and is desired to be secured by Letters
Patent of the United States is:
1. A fixing apparatus, comprising: a heater having a line shape
orthogonal to a direction in which a recording sheet carrying an
unfixed toner image formed with toner in accordance with image
information is transferred; an endless belt configured to be
rotated with an inner surface thereof sliding over a surface of
said heater; a pressure roller arranged at a position opposite to
said heater relative to said endless belt, said pressure roller
being held for rotation in contact with said endless belt under
pressure to form a nip therebetween; and a heater controller
configured to energize said heater in accordance with said image
information, wherein, when said recording sheet is brought to said
nip with said unfixed toner image facing said endless belt, said
pressure roller applies pressure to said recording sheet against
said endless belt so that said unfixed toner image is fixed on said
recording sheet with heat by said heater as said recording sheet is
transferred by movement of said endless belt and said pressure
roller.
2. A fixing apparatus as defined in claim 1, wherein said toner
includes a resin as a main adhesive agent and has properties of a
softening or melting point in a range between 50.degree. C. and
160.degree. C. and a viscosity in a range between 10 [c poise] and
10.sup.13 [c poise] under a temperature above said softening or
melting point.
3. A fixing apparatus as defined in claim 1, wherein said heater
includes at least two parallel heating elements, each of which has
a line shape orthogonal to said direction in which said recording
sheet is transferred.
4. A fixing apparatus as defined in claim 3, wherein said heater
controller alternately energizes said at least two parallel heating
elements with alternating pulses.
5. A fixing apparatus as defined in claim 3, wherein said at least
two parallel heating elements are distant from each other by 10 mm
or less.
6. A fixing apparatus as defined in claim 2, wherein each of said
at least two parallel heating elements has a width in a range
between 0.01 mm and 5 mm.
7. A fixing apparatus as defined in claim 1, wherein said heater
includes a plurality of heating elements arranged in line in a
direction orthogonal to said direction in which said recording
sheet is transferred.
8. A fixing apparatus as defined in claim 7, wherein each of said
plurality of heating elements includes a thermal head.
9. A fixing apparatus as defined in claim 6, wherein said heater
controller selectively energizes said plurality of heating
elements.
10. A fixing apparatus as defined in claim 1, further comprising a
cooling mechanism configured to cool said toner image after said
toner image is fixed with heat by said heater on said recording
sheet.
11. A fixing apparatus as defined in claim 1, further comprising a
guide roller arranged at a position downstream from said heater in
said direction in which said recording sheet is transferred, said
guide roller being configured to support said endless belt and to
serve as a cooling mechanism configured to cool said toner image
after said toner image is fixed with heat by said heater on said
recording sheet.
12. A fixing apparatus as defined in claim 1, further comprising a
mechanism configured to cause said endless belt to tightly hold
said toner image and said recording sheet together until said toner
image is fixed on said recording sheet after said toner image is
subjected to the heat of said heater.
13. A fixing apparatus as defined in claim 1, wherein said heater
controller stops energizing said heater during a time when a
non-image region between two adjacent toner image lines in said
recording sheet is brought close to said heater.
14. A fixing apparatus as defined in claim 1, wherein said heater
controller energizes said heater during a time when a region of
said toner image in said recording sheet is brought close to said
heater.
15. A fixing apparatus as defined in claim 1, wherein said heater
controller energizes said heater with an electric power reduced by
5% or more during a time when a non-image region between two
adjacent toner image lines in said recording sheet is brought close
to said heater.
16. A fixing apparatus, comprising: heating means for heating an
unfixed toner image formed with toner on a recording sheet in
accordance with image information, said heating means having a line
shape orthogonal to a direction in which said recording sheet is
transferred; endless belt means for being rotated with an inner
surface thereof sliding over a surface of said heating means;
pressure roller means for being held for rotation in contact with
said endless belt means under pressure to form a nip therebetween,
said pressure roller means being arranged at a position opposite to
said heating means relative to said endless belt means; and heater
controlling means for energizing said heating means in accordance
with said image information, wherein, when said recording sheet is
brought to said nip with said unfixed toner image facing said
endless belt means, said pressure roller means applies pressure to
said recording sheet against said endless belt means so that said
unfixed toner image is fixed on said recording sheet with heat by
said heating means as said recording sheet is transferred by
movement of said endless belt means and said pressure roller
means.
17. A fixing apparatus as defined in claim 16, wherein said toner
includes a resin as a main adhesive agent and has properties of a
softening or melting point in a range between 50.degree. C. and
160.degree. C. and a viscosity in a range between 10 [c poise] and
10.sup.13 [c poise] under a temperature above said softening or
melting point.
18. A fixing apparatus as defined in claim 16, wherein said heating
means includes at least two parallel heating elements, each of
which has a line shape orthogonal to said direction in which said
recording sheet is transferred.
19. A fixing apparatus as defined in claim 18, wherein said heater
controlling means alternately energizes said at least two parallel
heating elements with alternating pulses.
20. A fixing apparatus as defined in claim 18, wherein said at
least two parallel heating elements are distant from each other by
10 mm or less.
21. A fixing apparatus as defined in claim 17, wherein each of said
at least two parallel heating elements has a width in a range
between 0.01 mm and 5 mm.
22. A fixing apparatus as defined in claim 16, wherein said heating
means includes a plurality of heating elements arranged in line in
a direction orthogonal to said direction in which said recording
sheet is transferred.
23. A fixing apparatus as defined in claim 22, wherein each of said
plurality of heating elements includes a thermal head.
24. A fixing apparatus as defined in claim 21, wherein said heater
controlling means selectively energizes said plurality of heating
elements.
25. A fixing apparatus as defined in claim 16, further comprising
cooling means for cooling said toner image after said toner image
is fixed with heat by said heating means on said recording
sheet.
26. A fixing apparatus as defined in f claim 16, further comprising
guide roller means for supporting said endless belt means and
serving as cooling means for cooling said toner image after said
toner image is fixed with heat by said heating means on said
recording sheet, said guide roller being arranged at a position
downstream from said heating means in said direction in which said
recording sheet is transferred.
27. A fixing apparatus as defined in claim 16, further comprising
means for causing said endless belt means to tightly hold said
toner image and said recording sheet together until said toner
image is fixed on said recording sheet after said toner image is
subjected to the heat of said heating means.
28. A fixing apparatus as defined in claim 16, wherein said heater
controlling means stops energizing said heating means during a time
when a non-image region between two adjacent toner image lines in
said recording sheet is brought close to said heating means.
29. A fixing apparatus as defined in claim 16, wherein said heater
controlling means energizes said heating means during a time when a
region of said toner image in said recording sheet is brought close
to said heating means.
30. A fixing apparatus as defined in claim 16, wherein said heater
controlling means energizes said heating means with an electric
power reduced by 5% or more during a time when a non-image region
between two adjacent toner image lines in said recording sheet is
brought close to said heating means.
31. A fixing method of image forming, comprising the steps of:
forming a nip between an endless belt and a pressure roller which
are held for rotation in contact with each other under pressure;
proving a heater at position inside said endless belt, in contact
with said endless belt, and opposite to said pressure roller
relative to said endless belt, said heater having a line shape
orthogonal to a direction in which a recording sheet having an
unfixed toner image formed with toner in accordance with image
information is transferred; rotating said endless belt and said
pressure roller, said endless belt sliding over a surface of said
heater by rotation; transferring said recording sheet to said nip,
said recording sheet being in an orientation in which said toner
image faces said endless belt; and energizing said heater in
accordance with said image information when said toner image is
brought to said heater.
32. A fixing method as defined in claim 31, wherein said toner
includes a resin as a main adhesive agent and has properties of a
softening or melting point in a range between 50.degree. C. and
160.degree. C. and a viscosity in a range between 10 [c poise] and
10.sup.13 [c poise] under a temperature above said softening or
melting point.
33. A fixing method as defined in claim 31, wherein said heater
includes at least two parallel heating elements, each of which has
a line shape orthogonal to said direction in which said recording
sheet is transferred.
34. A fixing method as defined in claim 33, wherein said energizing
step alternately energizes said at least two parallel heating
elements with alternating pulses.
35. A fixing method as defined in claim 33, wherein said at least
two parallel heating elements are distant from each other by 10 mm
or less.
36. A fixing apparatus as defined in claim 32, wherein each of said
at least two parallel heating elements has a width in a range
between 0.01 mm and 5 mm.
37. A fixing method as defined in claim 31, wherein said heater
includes a plurality of heating elements arranged in line in a
direction orthogonal to said direction in which said recording
sheet is transferred.
38. A fixing method as defined in claim 37, wherein each of said
plurality of heating elements includes a thermal head.
39. A fixing method as defined in claim 36, wherein said energizing
step selectively energizes said plurality of heating elements.
40. A fixing method as defined in claim 31, further comprising a
cooling step for cooling said toner image after said toner image is
fixed with heat by said heating step on said recording sheet.
41. A fixing method as defined in claim 31, further comprising a
providing step for providing a guide roller for supporting said
endless belt and for serving as a cooling member for cooling said
toner image after said toner image is fixed with heat by said
heating step on said recording sheet, said guide roller being
arranged at a position downstream from said heater in said
direction in which said recording sheet is transferred.
42. A fixing method as defined in claim 31, further comprising a
providing step of providing a member for causing said endless belt
to tightly hold said toner image and said recording sheet together
until said toner image is fixed on said recording sheet after said
toner image is subjected to the heat of said heating step.
43. A fixing method as defined in claim 31, wherein said energizing
step stops energizing said heater during a time when a non-image
region between two adjacent toner image lines in said recording
sheet is brought close to said heater.
44. A fixing method as defined in claim 31, wherein said energizing
step energizes said heater during a time when a region of said
toner image in said recording sheet is brought close to said
heater.
45. A fixing method as defined in claim 31, wherein said energizing
step energizes said heater with an electric power reduced by 5% or
more during a time when a non-image region between two adjacent
toner image lines in said recording sheet is brought close to said
heater.
46. An image forming apparatus, comprising: an image forming
mechanism configured to form a toner image with toner on a
recording sheet in accordance with image information; a heater
having a line shape orthogonal to a direction in which said
recording sheet carrying an unfixed toner image formed by said
image forming mechanism is transferred; an endless belt configured
to be rotated with an inner surface thereof sliding over a surface
of said heater; a pressure roller arranged at a position opposite
to said heater relative to said endless belt, said pressure roller
being held for rotation in contact with said endless belt under
pressure to form a nip therebetween; and a heater controller
configured to energize said heater in accordance with said image
information, wherein, when said recording sheet is brought to said
nip with said unfixed toner image facing said endless belt, said
pressure roller applies pressure to said recording sheet against
said endless belt so that said unfixed toner image is fixed on said
recording sheet with heat by said heater as said recording sheet is
transferred by movement of said endless belt and said pressure
roller.
47. An image forming apparatus as defined in claim 45, wherein said
toner includes a resin as a main adhesive agent and has properties
of a softening or melting point in a range between 50.degree. C.
and 160.degree. C. and a viscosity in a range between 10 [c poise]
and 10.sup.13 [c poise] under a temperature above said softening or
melting point.
48. An image forming apparatus as defined in claim 45, wherein said
heater includes at least two parallel heating elements, each of
which has a line shape orthogonal to said direction in which said
recording sheet is transferred.
49. An image forming apparatus as defined in claim 48, wherein said
heater controller alternately energizes said at least two parallel
heating elements with alternating pulses.
50. An image forming apparatus as defined in claim 48, wherein said
at least two parallel heating elements are distant from each other
by 10 mm or less.
51. An image forming apparatus as defined in claim 47, wherein each
of said at least two parallel heating elements has a width in a
range between 0.01 mm and 5 mm.
52. An image forming apparatus as defined in claim 46, wherein said
heater includes a plurality of heating elements arranged in line in
a direction orthogonal to said direction in which said recording
sheet is transferred.
53. An image forming apparatus as defined in claim 52, wherein each
of said plurality of heating elements includes a thermal head.
54. An image forming apparatus as defined in claim 51, wherein said
heater controller selectively energizes said plurality of heating
elements.
55. An image forming apparatus as defined in claim 46, further
comprising a cooling mechanism configured to cool said toner image
after said toner image is fixed with heat by said heater on said
recording sheet.
56. An image forming apparatus as defined in claim 46, further
comprising a guide roller arranged at a position downstream from
said heater in said direction in which said recording sheet is
transferred, said guide roller being configured to support said
endless belt and to serve as a cooling mechanism configured to cool
said toner image after said toner image is fixed with heat by said
heater on said recording sheet.
57. An image forming apparatus as defined in claim 46, further
comprising a mechanism configured to cause said endless belt to
tightly hold said toner image and said recording sheet together
until said toner image is fixed on said recording sheet after said
toner image is subjected to the heat of said heater.
58. An image forming apparatus as defined in claim 46, wherein said
heater controller stops energizing said heater during a time when a
non-image region between two adjacent toner image lines in said
recording sheet is brought close to said heater.
59. An image forming apparatus as defined in claim 46, wherein said
heater controller energizes said heater during a time when a region
of said toner image in said recording sheet is brought close to
said heater.
60. An image forming apparatus as defined in claim 46, wherein said
heater controller energizes said heater with an electric power
reduced by 5% or more during a time when a non-image region between
two adjacent toner image lines in said recording sheet is brought
close to said heater.
61. An image forming apparatus, comprising: image forming means for
forming a toner image with toner on a recording sheet in accordance
with image information; heating means for heating an unfixed toner
image formed with toner on a recording sheet in accordance with
image information, said heating means having a line shape
orthogonal to a direction in which said recording sheet is
transferred; endless belt means for being rotated with an inner
surface thereof sliding over a surface of said heating means;
pressure roller means for being held for rotation in contact with
said endless belt means under pressure to form a nip therebetween,
said pressure roller means being arranged at a position opposite to
said heating means relative to said endless belt means; and heater
controlling means for energizing said heating means in accordance
with said image information, wherein, when said recording sheet is
brought to said nip with said unfixed toner image facing said
endless belt means, said pressure roller means applies pressure to
said recording sheet against said endless belt means so that said
unfixed toner image is fixed on said recording sheet with heat by
said heating means as said recording sheet is transferred by
movement of said endless belt means and said pressure roller
means.
62. An image forming apparatus as defined in claim 61, wherein said
toner includes a resin as a main adhesive agent and has properties
of a softening or melting point in a range between 50.degree. C.
and 160.degree. C. and a viscosity in a range between 10 [c poise]
and 10.sup.13 [c poise] under a temperature above said softening or
melting point.
63. An image forming apparatus as defined in claim 61, wherein said
heating means includes at least two parallel heating elements, each
of which has a line shape orthogonal to said direction in which
said recording sheet is transferred.
64. An image forming apparatus as defined in claim 63, wherein said
heater controlling means alternately energizes said at least two
parallel heating elements with alternating pulses.
65. An image forming apparatus as defined in claim 63, wherein said
at least two parallel heating elements are distant from each other
by 10 mm or less.
66. An image forming apparatus as defined in claim 62, wherein each
of said at least two parallel heating elements has a width in a
range between 0.01 mm and 5 mm.
67. An image forming apparatus as defined in claim 61, wherein said
heating means includes a plurality of heating elements arranged in
line in a direction orthogonal to said direction in which said
recording sheet is transferred.
68. An image forming apparatus as defined in claim 67, wherein each
of said plurality of heating elements includes a thermal head.
69. An image forming apparatus as defined in claim 66, wherein said
heater controlling means selectively energizes said plurality of
heating elements.
70. An image forming apparatus as defined in claim 61, further
comprising cooling means for cooling said toner image after said
toner image is fixed with heat by said heating means on said
recording sheet.
71. An image forming apparatus as defined in claim 61, further
comprising guide roller means for supporting said endless belt
means and serving as cooling means for cooling said toner image
after said toner image is fixed with heat by said heating means on
said recording sheet, said guide roller being arranged at a
position downstream from said heating means in said direction in
which said recording sheet is transferred.
72. An image forming apparatus as defined in claim 61, further
comprising means for causing said endless belt means to tightly
hold said toner image and said recording sheet together until said
toner image is fixed on said recording sheet after said toner image
is subjected to the heat of said heating means.
73. An image forming apparatus as defined in claim 61, wherein said
heater controlling means stops energizing said heating means during
a time when a non-image region between two adjacent toner image
lines in said recording sheet is brought close to said heating
means.
74. An image forming apparatus as defined in claim 61, wherein said
heater controlling means energizes said heating means during a time
when a region of said toner image in said recording sheet is
brought close to said heating means.
75. An image forming apparatus as defined in claim 61, wherein said
heater controlling means energizes said heating means with an
electric power reduced by 5% or more during a time when a non-image
region between two adjacent toner image lines in said recording
sheet is brought close to said heating means.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method and apparatus for
image forming, and more particularly to a method and apparatus for
image forming that is capable of performing an effective fixing
process.
[0003] 2. Description of the Related Art
[0004] Under an increasing demand for conservation of natural
resources and saving energy in the scope of a global environment
protection, considerable efforts in reducing consumption of
electric power are made in the field of electrophotographic image
forming apparatuses such as copying machines, facsimile machines,
printers, plotters, and so on. Among various processes of image
forming, a fixing process particularly consumes a great amount of
electric power and a technique of a low temperature fixing is
expedited in this field. To succeed in the low temperature fixing,
it is necessarily needed to lower a softening or melting point of
toner. A thermoplastic resin included in the toner has a character
that lower the softening or melting point lower a melting
viscosity. This character is based on a fact that the softening or
melting point of a thermoplastic resin is determined by various
factors such as molecular weight, distribution of molecular weight,
the level of crystallization, the level of bridging, intermolecular
force, and so forth. Therefore, in order to lower the softening or
melting point of a thermoplastic resin without changing its
structure, it is needed that the molecular weight or the level of
bridging is reduced or that the distribution of molecular weight is
narrowed. Since the distribution of molecular weight has a lower
limitation which is determined by a storage limitation of the
resin, it is narrowed when the molecular weight is reduced.
[0005] In general, when molecular weight is reduced, chains of
molecules are shortened and the connections between the molecules
are loosened. Therefore, the melting viscosity is lowered. Also,
when the distribution of molecular weight is narrowed, the
connections between the molecules are loosened and therefore the
melting viscosity is lowered. Further, when the level of bridging
between molecules is lowered, each molecule becomes easy to move
and therefore the melting viscosity of the molecules is
lowered.
[0006] For example, a published Japanese examined patent
application No. 51-29825 (1976) describes a fixing method which
performs a fixing process using toner that has a lowered melting
viscosity, as described above, without causing an offset. The
offset in the fixing process is a problematic phenomenon in which
toner is undesirably deposited on a part of a fixing roller by
loosing its character of cohesion when melted. The fixing of toner
is performed when the toner is in a rubber state. That is, as a
temperature rises, the toner resin begins to be softened and its
viscosity is lowered. Then, the toner resin is brought to a state
of rubber. As far as being in the rubber state, the toner resin
maintains a relatively high cohesion and does not cause the offset
problem.
[0007] A Japanese Patent, No. 2516886, describes an apparatus for
heating an image using the above-mentioned technique. This
apparatus includes a line-shaped heating member based on a heating
member described in the above-mentioned published Japanese examined
patent application, No. 51-29825 (1976), and is characterized by a
feature in that the line-shaped heating member is energized with a
pulse signal. This feature attempts to eliminate a residual heat
needed for reduction of a standby time and to reduce emission of an
extra amount of heat inside the apparatus.
[0008] The above-mentioned background techniques and apparatuses,
however, may only be effective when the apparatus processes a small
number of images or when the apparatus is almost out of busy state.
When a large number of images are processed, the recording sheets
take a great amount of heat. This causes a loss of a great amount
of energy, regardless of whether a roller-shaped or line-shaped
heating member is used.
[0009] However, in most cases, an image to be actually printed on a
recording sheet has a substantial area in the range between 2% and
10% relative to a recording area in a recording sheet. This means
that heat is taken also by a 90% to 98% area of a recording sheet
without being used. For example, a text image that has lines of
characters typically includes non-image spaces between the lines
and the heat applied to these non-image spaces are not used.
[0010] Since the above-mentioned background techniques and
apparatuses employ the toner having a relatively high softening or
melting point, a partial application of heat to an image area in a
recording sheet causes a fixing mechanism and a recording sheet to
be regionally deformed. As a result, the recording sheet is
transferred not in a properly straight manner or has wrinkles due
to distortion.
SUMMARY OF THE INVENTION
[0011] The present application describes a novel fixing apparatus.
In one example, a novel fixing apparatus includes a heater, an
endless belt, a pressure roller, and a heater controller. The
heater has a line shape orthogonal to a direction in which a
recording sheet carrying an unfixed toner image formed with toner
in accordance with image information is transferred. The endless
belt is configured to be rotated with an inner surface thereof
sliding over a surface of the heater. The pressure roller is
arranged at a position opposite to the heater relative to the
endless belt and is held for rotation in contact with the endless
belt under pressure to form a nip therebetween. The heater
controller is configured to energize the heater in accordance with
the image information. In this novel fixing apparatus, when the
recording sheet is brought to the nip with the unfixed toner image
facing the endless belt, the pressure roller applies pressure to
the recording sheet against the endless belt so that the unfixed
toner image is fixed on the recording sheet with heat by the heater
as the recording sheet is transferred by movement of the endless
belt and the pressure roller.
[0012] The toner may include a resin as a main adhesive agent and
has properties of a softening or melting point in a range between
50.degree. C. and 160.degree. C. and a viscosity in a range between
10 [c poise] and 10.sup.13 [c poise] under a temperature above the
softening or melting point.
[0013] The heater may include at least two parallel heating
elements, each of which has a line shape orthogonal to the
direction in which the recording sheet is transferred.
[0014] The heater controller may alternately energize the
above-mentioned at least two parallel heating elements with
alternating pulses.
[0015] The above-mentioned at least two parallel heating elements
may be distant from each other by 10 mm or less.
[0016] Each of the at least two parallel heating elements may have
a width in a range between 0.01 mm and 5 mm.
[0017] The heater may include a plurality of heating elements
arranged in line in a direction orthogonal to the direction in
which the recording sheet is transferred.
[0018] Each of the plurality of heating elements may include a
thermal head.
[0019] The heater controller may selectively energize the plurality
of heating elements.
[0020] The above-mentioned fixing apparatus may further include a
cooling mechanism configured to cool the toner image after the
toner image is fixed with heat by the heater on the recording
sheet.
[0021] The above-mentioned fixing apparatus may further include a
guide roller arranged at a position downstream from the heater in
the direction in which the recording sheet is transferred, the
guide roller being configured to support the endless belt and to
serve as a cooling mechanism configured to cool the toner image
after the toner image is fixed with heat by the heater on the
recording sheet.
[0022] The above-mentioned fixing apparatus may further include a
mechanism configured to cause the endless belt to tightly hold the
toner image and the recording sheet together until the toner image
is fixed on the recording sheet after the toner image is subjected
to the heat of the heater.
[0023] The heater controller may stop energizing the heater during
a time when a non-image region between two adjacent toner image
lines in the recording sheet is brought close to the heater.
[0024] The heater controller may energize the heater during a time
when a region of the toner image in the recording sheet is brought
close to the heater.
[0025] The heater controller may energize the heater with an
electric power reduced by 5% or more during a time when a non-image
region between two adjacent toner image lines in the recording
sheet is brought close to the heater.
[0026] The present invention further provides a novel fixing method
of image forming. In one example, a novel fixing method of image
forming includes the steps of forming, proving, rotating,
transferring and energizing. The forming step forms a nip between
an endless belt and a pressure roller which are held for rotation
in contact with each other under pressure. The proving step
provides a heater at position inside the endless belt, in contact
with the endless belt, and opposite to the pressure roller relative
to the endless belt. The above-mentioned heater has a line shape
orthogonal to a direction in which a recording sheet having an
unfixed toner image formed with toner in accordance with image
information is transferred. The rotating step rotates the endless
belt and the pressure roller. In this case, the endless belt slides
over a surface of the heater by rotation. The transferring step
transfers the recording sheet to the nip. The recording sheet is in
an orientation in which the toner image faces the endless belt. The
energizing step energizes the heater in accordance with the image
information when the toner image is brought to the heater.
[0027] The present invention further provides a novel image forming
apparatus. In one example, a novel image forming apparatus includes
an image forming mechanism, a heater, an endless belt, a pressure
roller, and a heater controller. The image forming mechanism is
configured to form a toner image with toner on a recording sheet in
accordance with image information. The heater has a line shape
orthogonal to a direction in which the recording sheet carrying an
unfixed toner image formed by the image forming mechanism is
transferred. The endless belt is configured to be rotated with an
inner surface thereof sliding over a surface of the heater. The
pressure roller is arranged at a position opposite to the heater
relative to the endless belt and is held for rotation in contact
with the endless belt under pressure to form a nip therebetween.
The heater controller is configured to energize the heater in
accordance with the image information. In the above-mentioned image
forming apparatus, when the recording sheet is brought to the nip
with the unfixed toner image facing the endless belt, the pressure
roller applies pressure to the recording sheet against the endless
belt so that the unfixed toner image is fixed on the recording
sheet with heat by the heater as the recording sheet is transferred
by movement of the endless belt and the pressure roller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] A more complete appreciation of the present invention and
many of the attendant advantages thereof will be readily obtained
as the same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0029] FIG. 1 is a schematic diagram of an image forming apparatus
including a fixing apparatus according to an embodiment of the
present invention;
[0030] FIG. 2 is a schematic diagram of the fixing apparatus
included in the image forming apparatus of FIG. 1;
[0031] FIG. 3 is a schematic diagram of a power controller included
in the image forming apparatus of FIG. 1;
[0032] FIG. 4 is a schematic diagram of a modified fixing apparatus
based on the fixing apparatus of FIG. 2;
[0033] FIGS. 5A-5C are time charts for explaining a relationship
between a heater driving signal and a necessary driving power and a
relationship between the heater driving signal that forms a high
signal with a plurality of pulses and a pulse integrate wave signal
as a conveniently expressed signal;
[0034] FIG. 6 is an illustration for explaining a way how an energy
of electric power is saved by a fixing operation of the fixing
apparatus of FIG. 2;
[0035] FIG. 7 is an illustration for explaining a modification of
the fixing operation explained with reference to FIG. 6;
[0036] FIG. 8 is a schematic diagram of an image forming apparatus
including another fixing apparatus according to an embodiment of
the present invention;
[0037] FIG. 9 is a schematic diagram of the fixing apparatus
included in the image forming apparatus of FIG. 8;
[0038] FIG. 10 is a schematic diagram of a power controller
included in the image forming apparatus of FIG. 8;
[0039] FIGS. 11 and 12 are schematic diagrams for explaining a
modified fixing apparatus based on the fixing apparatus of FIG.
9;
[0040] FIGS. 13A and 13B are illustrations for explaining a way how
an energy of electric power is saved by a fixing operation of the
fixing apparatus of FIG. 9;
[0041] FIGS. 14A and 14B are illustrations for explaining a
modification of the fixing operation explained with reference to
FIG. 13A;
[0042] FIG. 15 is an illustration for explaining another
modification of the fixing operation explained with reference to
FIG. 13A;
[0043] FIG. 16 is a schematic diagram of an image forming apparatus
including another fixing apparatus according to an embodiment of
the present invention;
[0044] FIG. 17 is a schematic diagram of the fixing apparatus
included in the image forming apparatus of FIG. 16;
[0045] FIG. 18 is a schematic diagram of a power controller
included in the image forming apparatus of FIG. 16;
[0046] FIG. 19 is a schematic diagram for explaining a modified
fixing apparatus based on the fixing apparatus of FIG. 17;
[0047] FIG. 20 is an illustration for explaining a way how an
energy of electric power is saved by a fixing operation of the
fixing apparatus of FIG. 17; and
[0048] FIG. 21 is an illustration for explaining a modification of
the fixing operation explained with reference to FIG. 20.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0049] In describing preferred embodiments of the present invention
illustrated in the drawings, specific terminology is employed for
the sake of clarity. However, the present invention is not intended
to be limited to the specific terminology so selected and it is to
be understood that each specific element includes all technical
equivalents which operate in a similar manner.
[0050] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts throughout the
several views, and more particularly to FIG. 1 thereof, an image
forming apparatus 100 according to an embodiment of the present
invention is explained. FIG. 1 shows a main portion of the image
forming apparatus 100 that performs an image forming operation in
accordance with an electrophotographic method. As illustrated in
FIG. 1, the image forming apparatus 100 includes a photoconductor
1, a charging unit 2, an optical writing unit 3, a development unit
4, a transfer unit 5, a cleaning unit 6, and a discharging unit 7.
The photoconductor 1 is a photosensitive and photoconductive
member, having a drum-like shape, and is mounted at the center
among above-mentioned various components. The photoconductor 1 is
rotated in a direction indicated by an arrow and serves as an image
carrying member. The charging unit 2 performs a charging process in
which the surface of the photoconductor 1 is evenly charged. The
optical writing unit 3 emits a laser beam (LB) and controls it to
write an electrostatic image on the surface of the photoconductor
1, which process is referred to as an optical writing process. The
development unit 4 performs a development process for developing
the electrostatic image into a visual image with toner. The
transfer unit 5 performs a transfer process for transferring the
toner image formed on the surface of the photoconductor 1 onto a
recording sheet P. The cleaning unit 6 performs a cleaning process
for cleaning residual toner and dust off the surface of the
photoconductor 1. The discharging unit 7 performs a discharging
process for discharging a remaining charge on the photoconductor
1.
[0051] The image forming apparatus 100 further includes a sheet
cassette 8, a sheet feed roller 9, a pair of registration rollers
10, and a fixing unit 11. The sheet cassette 8 stores a plurality
of recording sheets P. The sheet feed roller 9 picks up a recording
sheet P from the sheet cassette 8 and transfers it towards the
registration roller 10 that transfers the recording sheet P towards
the photoconductor 1 in synchronism with a rotational movement of
the photoconductor 1. The fixing unit 11 performs a fixing process
for fixing the toner image on the recording sheet P after a
completion of the transfer process. The recording sheet P is
transferred through a sheet path arranged along a dotted-line with
an arrow, as shown in FIG. 1.
[0052] The development unit 4 uses toner that includes resin as a
main adhesive element and has a softening or melting point in a
range between 50.degree. C. and 160.degree. C. and a viscosity in a
range of from 10 [c poise] to 10.sup.13 [c poise] at a temperature
above the softening or melting point.
[0053] As shown in FIG. 2, the fixing unit 11 includes a heater 12,
endless belts 13 and 14, a pressure roller 15, and guide rollers
16-18. The heater 12 includes a line heating member, i.e., a
thermal head or a heater, and is arranged in a way such that the
longitudinal side thereof is orthogonal to a sheet transfer
direction in which the recording sheet P is fed. The endless belt
13 is extended under pressure between the guide rollers 17 and 18
and contacts the heater 12. The endless belt 13 is rotated in a
direction indicated by an arrow. The pressure roller 15 is disposed
at a position facing the heater 12 via the endless belts 13 and 14.
When the recording sheet P is present between the endless belts 13
and 14, the pressure roller 15 applies pressure to the recording
sheet P against the heater 12 via the endless belts 13 and 14. The
endless belt 14 is extended under pressure between the pressure
roller 15 and the guide roller 16.
[0054] In the above-described fixing unit 11, a toner image T on
the recording sheet P is heated by the heater 12 via the endless
belt 13 when the recording sheet P is fed into the gap between the
endless belts 13 and 14. After that, the recording sheet P is
subjected to a cooling process by which the toner image T is firmly
fixed to the recording sheet P and is then separated from the
endless belt 14. At least one of the guide rollers 16 and 18,
arranged downstream from the heater 12 in the sheet transfer
direction, is made of metal having a relatively high thermal
conductivity and serves as a driving roller and a cooling roller.
After a completion of the heat fixing process, the toner image T,
the recording sheet P, and the endless belt 13 are cooled by the
guide rollers 16 and 18. The recording sheet P is made close
contact with the endless belts 13 and 14 while it is held by these
endless belts 13 and 14. That is, the toner image T deposited on
the recording sheet P is sealed by the endless belt 13 during the
time the recording sheet P is processed by the fixing unit 11. The
toner image T is therefore not removed from the recording sheet P
when heated. And, the recording sheet P is separated from the
endless belt 13 after the toner image T is sufficiently cooled and
fixed on the recording sheet P so that the toner image T is not
left deposited on the endless belt 13. Thus, the fixing unit 11
outputs an image in a stable quality without causing the
offset.
[0055] The image forming apparatus 100 further includes a power
controller 20, as shown in FIG. 1. The power controller 20 controls
a signal of an electric power to be input to the heater 12. FIG. 3
shows a block diagram of the power controller 20. The power
controller 20 includes a power source 21, a control unit 22, and a
fixing power control circuit 23. The control unit 22 controls the
entire operations of the image forming apparatus 100. The heater 12
is connected to the fixing power control circuit 23 to which the
electric power is supplied from the power source 21 under the
control of the control unit 22. More specifically, the fixing power
control circuit 23 generates a heater driving signal for driving
the heater 12 in accordance with the corresponding image
information sent from the control unit 22 so that the heater 12 is
heated up and performs the fixing process for fixing the toner
image deposited on the recording sheet which is presently processed
by the fixing unit 11.
[0056] The above-mentioned control unit 22 may either be separated
from or unified with the power controller 20.
[0057] FIG. 4 illustrates an alternative structure of the fixing
unit 11. In this structure, a pressure roller 135 that serves as a
pressure roller and a driving roller contacts an endless belt 133
under pressure to form a nip therebetween and drives the endless
belt 133 with friction so that the endless belt 133 rotates in a
direction indicated by an arrow. Therefore, when the recording
sheet P is fed into the gap between the endless belt 133 and the
pressure roller 135, the pressure roller 135 presses the recording
sheet P against a heater 132 via the endless belt 133. The toner
image T and the recording sheet P are cooled by themselves, as
indicated by an arrow C, after a completion of the heat fixing
process.
[0058] Referring to FIGS. 5A-5C, a description is made for the
heater driving signal generated by the fixing power control unit 23
of the power controller 20. FIG. 5A demonstrates a relationship
between a rectangular wave signal A1 for driving a heater (i.e.,
the heater 12) and a temperature curve B1 of the heater driven by
the rectangular wave signal A1. This indicates that, when the
heater is driven by the rectangular wave signal A1, the heater
raises its temperature B1 far above a temperature C necessary for
the heat fixing process and is eventually damaged. To make the
temperature curve formed in a rectangular shape equivalent to the
driving signal, driving the heater with a signal having a plurality
of pulses is effective, as shown in FIG. 5B. In this case, the
heater is driven by a signal A2 having a plurality of pulses and a
resultant temperature curve B2 of the heater is formed like in a
rectangular shape almost equivalent to the signal A2 having its
peak level close to the temperature C necessary for the heat fixing
process. Therefore, the fixing power control unit 23 is configured
to generate the heater driving signal that has a plurality of
pulses, as shown in FIG. 5B. Accordingly, the heater driving signal
actually used in the image forming apparatus 100 has a plurality of
pulses. However, for the sake of simplicity, such a signal having a
plurality of pulses is expressed hereinafter as a pulse integrate
wave signal that appears to be a simple rectangular wave signal, as
shown in FIG. 5C, wherein the signal having a plurality of pulses
is indicated as A3 and the signal having a pulse integral wave is
indicated as A.sub.int.
[0059] The above-mentioned pulses included in the heater driving
signal generated by the fixing power control unit 23 may either
have a constant or varied distant from each other and may either
have a constant or varied length.
[0060] Referring to FIG. 6, a way how an energy of electric power
is saved by the fixing operation of the above-described fixing unit
11 is explained. In the image forming apparatus 100, the heater
driving signal for driving the heater 12, or the heater 32, has
high and low levels and, when at a high, it includes a plurality of
pulses. This high level signal is expressed as a pulse integral
wave signal as described above. Hereinbelow, the heaters 12 and 32
are represented by the heater 12. FIG. 6 represents a relationship
among positions of the heater 12, the recording sheet P, and the
toner images T1-T5 and a relationship between the heater driving
signal expressed as the signal A.sub.int and the toner images
T1-T5, at the same time. The heater 12 is heated when the heater
driving signal or the signal A.sub.int is activated, as shown in
FIG. 6. When the signal A.sub.int is activated to a high the heater
12 is turned on for heating and when the signal A.sub.int is
deactivated to a low the heater 12 is turned off.
[0061] FIG. 6 attempts to express a way how the energy of the
electric power for the fixing process is saved when the recording
sheet P having toner images T1-T5, for example, is processed by the
fixing unit 11. As shown in FIG. 6, the toner images T1-T5 have
different in size from each other, for example. During the time the
recording sheet P passes through the fixing unit 11, the signal
A.sub.int is raised to a high so as to drive the heater 12 each
time one of the toner images T1-T5 is brought close to the heater
12. The signal A.sub.int is fallen to a low so as to turn off the
heater 12 when each of the toner images T1-T5 is brought away from
the heater 12 as the recording sheet P is being transferred in the
fixing unit 11. During the time a white area having no toner image
in the recording sheet P is brought to be passing by the heater 12,
the signal A.sub.int is not raised to a high and therefore the
heater 12 is not driven.
[0062] In this way, the fixing unit 11 can greatly save the energy
of electric power through its fixing operation, as described above.
This would be readily understood by comparing it with a case where
the heater 12 is always driven with a continuous driving signal.
For example, a text image that has lines of characters typically
includes spaces between the lines. When such an image is processed
by the fixing unit 11, the signal A.sub.int is held at a low at
which no electric energy is consumed during the time periods
corresponding to these spaces. Thus, a great amount of electric
power can be saved.
[0063] FIG. 7 shows a modification of the fixing power control
performed by the fixing power control unit 23. As indicated in FIG.
7, the signal A.sub.int has three levels; a zero level, a white
level, and a black level. The signal A.sub.int is held at the zero
level so as not to drive the heater 12 during the time the
recording sheet P is not present in the fixing unit 11. The signal
A.sub.int is raised to the white level so as to pre-heat the heater
12 when the recording area of the recording sheet P is brought
close to the heater 12. The signal A.sub.int is raised from the
white level to the black level so as to heat the heater 12 when the
toner image T1 is brought close to the heater 12 and is fallen back
to the white level so as to pre-heat the heater 12 when the toner
image T1 is brought away from the heater 12. The signal A.sub.int
is again raised to the black level so as to heat the heater 12 when
the next toner image T2 is brought close to the heater 12 and is
fallen back to the white level so as to pre-heat the heater 12 when
that toner image T2 is brought away from the heater 12. This cycle
is repeated for each toner image. The signal A.sub.int is fallen
down to the zero level so as to turn off the heater 12 when the
recording area of the recording sheet P brought away from the
heater 12.
[0064] The black level is a level in which the heater 12 is driven
in a full power. The white level is a level at which the heater 12
is pre-heated with an electric power having a reduction by 5% or
more from the power of the black level.
[0065] With the above modified fixing power control, the heater 12
is improved in responsivity while achieving the energy saving.
[0066] Next, another image forming apparatus 200 according to the
embodiment of the present invention is explained with reference to
FIGS. 8-10. As shown in FIG. 8, the image forming apparatus 200 is
similar to that of FIG. 1, except for a fixing unit 211 and a power
controller 220. The fixing unit 211 is, as shown in FIG. 9, similar
to the fixing unit 11 of FIG. 2, except for a heater 212 that
includes heating member 212a and 212b for heating the toner image
T. The power controller 220 is shown in FIG. 10 and is similar to
the power controller 20 of FIG. 3, except for a fixing power
control circuit 223. The fixing power control circuit 223 has
separate connections to the heating members 212a and 212b of the
heater 212, as shown in FIG. 10, and generates the heater driving
signals for driving the heating members 212a and 212b,
respectively, in accordance with the corresponding image
information sent from the control unit 22. Thereby, heating members
212a and 212b of the heater 212 are heated up to perform the fixing
process in accordance with the corresponding toner images deposited
on the recording sheet P which is presently processed in the fixing
unit 211. The above-mentioned heater driving signals are composed
of a plurality of pulses and are hereinafter expressed as the pulse
integrate wave signals A.sub.int-a and A.sub.int-b, as is the case
explained with reference to FIGS. 5A-5C.
[0067] It is noted that the above-described control unit 22 may
either be separated from or unified with the power controller
220.
[0068] Each of the heating member 212a and 212b of the heater 212
is a thermal head or a heater, for example, having a line shape,
and heats the toner image T. The heater 212 is arranged at a
position so that the heating members 212a and 212b are orthogonal
to the sheet transfer direction. The heating members 212a and 212b
are selectively driven by the fixing power control circuit 223 of
the power controller 220 such that the heating members 212a and
212b are not driven at the same time. The heating members 212a and
212b are desirably arranged with a distant smaller than 10 mm from
each other. The heater 212 is superior when the distant between the
heating members 212a and 212b is 6 mm or less, is more superior
when the distant is 4 mm or less, is far more superior when the
distant is 2 mm or less, and is extremely superior when the distant
is 1 mm or less. The width of each heating member is desirably
within a range of from 0.01 mm to 5 mm. The heater 212 is superior
when the width of each heating member is within a range between 0.1
mm and 4 mm, is more superior when the width is in a range between
0.2 mm and 2 mm, and far more superior when the width is within a
range between 0.5 mm to 1 mm.
[0069] In the above-described fixing unit 211, the toner image T on
the recording sheet P is heated by the heating members 212a and
212b of the heater 212 via the endless belt 13 when the recording
sheet P is fed into the gap between the endless belts 13 and 14.
After that, the recording sheet P is subjected to a cooling process
by which the toner image T is firmly fixed to the recording sheet P
and is then separated from the endless belt 14. At least one of the
guide rollers 16 and 18, arranged downstream from the heater 212 in
the sheet transfer direction, is made of metal having a relatively
high thermal conductivity and serves as a driving roller and a
cooling roller, as is the case with the fixing unit 11 of FIG. 2.
After a completion of the heat fixing process, the toner image T,
the recording sheet P, and the endless belt 13 are cooled by the
guide rollers 16 and 18. The recording sheet P is made close
contact with the endless belts 13 and 14 while it is held by these
endless belts 13 and 14. That is, the toner image T deposited on
the recording sheet P is sealed by the endless belt 13 during the
time the recording sheet P is processed by the fixing unit 211. The
toner image T is therefore not removed from the recording sheet P
when heated. And, the recording sheet P is separated from the
endless belt 13 after the toner image T is sufficiently cooled and
fixed on the recording sheet P so that the toner image T is not
left deposited on the endless belt 13. Thus, the fixing unit 211
outputs an image in a stable quality without causing the
offset.
[0070] In the fixing unit 211, the heater 212 may include one or
more additional heating members in addition to the heating members
212a and 212b.
[0071] FIG. 11 illustrates an alternative structure of the fixing
unit 211. In this structure, a pressure roller 235 that serves as a
pressure roller and a driving roller contacts an endless belt 233
under pressure to form a nip therebetween and drives the endless
belt 233 with friction so that the endless belt 233 rotates in a
direction indicated by an arrow. Therefore, when the recording
sheet P is fed into the gap between the endless belt 233 and the
pressure roller 235, the pressure roller 235 presses the recording
sheet P against a heater 232 via the endless belt 233. The toner
image T and the recording sheet P are cooled by themselves, as
indicated by an arrow C, after a completion of the heat fixing
process.
[0072] FIG. 12 demonstrates that, in the above-described
alternative structure of FIG. 11, the heater 232 includes heating
members 232a and 232b arranged orthogonal to the sheet transfer
direction and a cooling portion C arranged downstream from the
heating members 232a and 232b in the sheet transfer direction.
Further, the nip formed between the endless belt 233 and the
pressure roller 235 is extended from the heating area of the
heating members 232a and 232b to the cooling portion C, as
indicated by a letter N. Thereby, the toner image T on the
recording sheet P is sealed by the endless belt 233 during the time
the recording sheet P is processed through the fixing process. This
protects removal of the toner image T from the recording sheet P.
Then, the recording sheet P is subjected to the cooling process
when passing by the cooling portion C. After cooled and fixed, the
recording sheet P is separated from the endless belt 233. As a
result, the toner image T is not left deposited on the endless belt
13 through this heat fixing process. Thus, a highly stable quality
image is output without causing the offset.
[0073] In the above structure of FIGS. 11 and 12, the cooling
portion C may use any one of cooling by itself, cooling with air,
cooling with water, refrigerative including fluorocarbon, Peltier
element, and the like.
[0074] Further, in the above structure of FIGS. 11 and 12, the
heater 232 may include one or more additional heating members in
addition to the heating members 232a and 232b.
[0075] When the image forming process is performed in a high speed,
it affects the fixing process by the fixing unit such that an
increasing amount of heat is absorbed by the endless belt and
therefore the temperature of the heater needs to be increased.
However, the image forming apparatus 200 employs the heating
members 212a and 212b in the heater 212 to maintain a total amount
of heat unchanged without increasing the temperature of the heater.
Thus, the heating members of the heater are protected from the
damage caused by a high temperature. In the description below, two
heater driving signals for driving the heating members 212a and
212b of the heater 212 are expressed as pulse integral wave signals
A.sub.int-a and A.sub.int-b, respectively.
[0076] FIG. 13A expresses a way how the energy of the electric
power for the fixing process is saved when the recording sheet P
having toner images T1-T4, for example, is processed by the fixing
unit 211. In this case, the toner images T1-T4 have the same width
and length, as shown in FIG. 13A. During the time the recording
sheet P processed through the fixing unit 211, the signals
A.sub.int-a and A.sub.int-b are switched between the white and
black levels so as to drive the heating members 212a and 212b of
the heater 212 each time one of the toner images T1-T4 is brought
close to the respective heating members of the heater 212. Thereby,
the toner image T1 is heated and accordingly fixed on the recording
sheet P. The signals A.sub.int-a and A.sub.int-b are not raised and
therefore the heating members 212a and 212b of the heater 212 are
not driven during the time a white area having no toner image in
the recording sheet P is brought to be passing by the heater
212.
[0077] More specifically, a way of driving the heating members 212a
and 212b is explained with reference to FIG. 13B that shows an
enlarged part of FIG. 13A. That is, FIG. 13A shows an area circled
with a dotted line indicated by a letter D and this area is shown
in FIG. 13B in a manner enlarged in the sheet transfer direction.
When the toner image T1 is brought close to the heating member
212a, driving the heating member 212a has been started with at
least one precedent pulse of the signal A.sub.int-a. Likewise, when
the toner image T1 is brought close to the heating member 212b,
driving the heating member 212b has been started with at least one
precedent pulse of the signal A.sub.int-b.
[0078] As also shown in FIG. 13B, the pulses included in the
signals A.sub.int-a and A.sub.int-b are alternately raised to a
high but not at the same time. This leads to a great amount of
reduction of the power consumption. That is, in comparison with a
case where the signals A.sub.int-a and A.sub.int-b are raised to a
high at the same time, the power consumption per a unit time period
is saved to an extend approximately half of it. It is noted that
the experiment was conducted in which the amount of the power
consumption was 1200 watts when the signals A.sub.int-a and
A.sub.int-b are raised to a high at the same time but it was
reduced to 600 watts when the signals A.sub.int-a and A.sub.int-b
are alternately raised to a high.
[0079] Thus, the fixing unit 211 can greatly save the energy of
electric power through its fixing operation, as described above.
This would be readily understood by comparing it with a case where
the heating members 212a and 212b of the heater 212 are always
driven with continuous driving signals. For example, a text image
that has lines of characters typically includes spaces between the
lines. When such an image is processed by the fixing unit 211, the
signals A.sub.int-a and A.sub.int-b are held at a low at which no
electric energy is consumed during the time periods corresponding
to these spaces. Thus, a great amount of electric power can be
saved.
[0080] FIG. 14A shows a modification of the fixing power control
performed by the fixing power control unit 223. As in the case of
the fixing power control unit 23 of FIG. 3, each of the signals
A.sub.int-a and A.sub.int-b has three levels; a zero level, a white
level, and a black level. The signals A.sub.int-a and A.sub.int-b
are held at the zero level so as to deactivate the heating members
212a and 212b of the heater 212 when the recording sheet P is not
present in the fixing unit 211. The signals A.sub.int-a and
A.sub.int-b are raised to the white level so as to pre-heat the
heating members 212a and 212b of the heater 212 when the image area
of the recording sheet P is brought close to the heating members
212a and 212b of the heater 212 after the recording sheet P is fed
into the fixing unit 211. The signals A.sub.int-a and A.sub.int-b
are further raised to the black level so as to heat up the heating
members 212a and 212b, respectively, when the toner image T1 is
brought close to the heating members 212a and 212b. Then, the
signals A.sub.int-a and A.sub.int-b are fallen back to the white
level so as to pre-heat the heating members 212a and 212b,
respectively, when the toner image T1 is brought away from the
heating members 212a and 212b. The signals A.sub.int-a and
A.sub.int-b are again raised to the black level so as to heat the
heating members 212a and 212b, respectively, when the next toner
image T2 is brought close to the heating members 212a and 212b.
Then, the signals A.sub.int-a and A.sub.int-b are fallen back to
the white level so as to pre-heat the heating members 212a and
212b, respectively, when that toner image T2 is brought away from
the heating members 212a and 212b. This cycle is repeated until the
toner image T4 is brought away from the heating members 212a and
212b of the heater 212. After the toner image T4, the signals
A.sub.int-a and A.sub.int-b are fallen down to the zero level so as
to deactivate the heating members 212a and 212b, respectively, when
the image area of the recording sheet P is brought away from the
heating members 212a and 212b.
[0081] The black level is a level in which the heater 212 is driven
in a full power. The white level is a level in which the heater 212
is primarily heated with an electric power with a reduction of 5%
or more from the power of the black level.
[0082] FIG. 14B explains more specifically a way of driving the
heating members 212a and 212b. FIG. 14B shows an enlarged part of
FIG. 14A. That is, an area circled with a dotted line indicated by
a letter D shown in FIG. 14A is shown in FIG. 14B in a manner
enlarged in the sheet transfer direction. When the toner image T1
is brought close to the heating member 212a, driving the heating
member 212a has been started with at least one precedent pulse of
the signal A.sub.int-a which is raised from the white level to the
black level. Likewise, when the toner image T1 is brought close to
the heating member 212b, driving the heating member 212b has been
started with at least one precedent pulse of the signal A.sub.int-a
which is raised from the white level to the black level.
[0083] As also shown in FIG. 14B, the pulses included in the
signals A.sub.int-a and A.sub.int-b are alternately raised to a
high but not at the same time. This leads to a great amount of
reduction of the power consumption. That is, in comparison with a
case where the signals A.sub.int-a and A.sub.int-b are raised to a
high at the same time, the power consumption per a unit time period
is saved to an extend approximately half of it. It is noted that
the experiment was conducted in which the white level had a 5%
power reduction from the full power of the black level. In this
experiment, the amount of the power consumption was recorded as
1200 watts when the signals A.sub.int-a and A.sub.int-b are raised
to a high at the same time. However, the amount of the power
consumption was reduced to 570 watts when the signals A.sub.int-a
and A.sub.int-b are alternately raised. This is because the 5%
power reduction contributed for a further reduction of 30
watts.
[0084] Thus, the fixing unit 211 can greatly save the energy of
electric power through its fixing operation, as described above.
This would be readily understood by comparing it with a case where
the heating members 212a and 212b of the heater 212 are always
driven with continuous driving signals. For example, a text image
that has lines of characters typically includes spaces between the
lines. When such an image is processed by the fixing unit 211, the
signals A.sub.int-a and A.sub.int-b are held at the white level at
which an electric power can be reduced by 5% or more during the
time periods corresponding to the above-mentioned spaces. Thus, a
great amount of electric power can be saved.
[0085] With the above modified fixing power control, the heater 212
is improved in responsivity while achieving the energy saving.
[0086] FIG. 15 shows another modification of the fixing power
control performed by the fixing power control unit 223. This
modification is similar to that of FIG. 14A, except for the control
of the zero level before the toner image T1 and after the toner
image T4. More specifically, in this modification of FIG. 15,
during the time the recording area of the recording sheet P between
the leading edge of the recording sheet and the first toner image
T1 is brought close to the heating members, the signals A.sub.int-a
and A.sub.int-b are held at the zero level so as to deactivate the
heating members 212a and 212b. Also, the signals A.sub.int-a and
A.sub.int-b are held at the zero level so as to deactivate the
heating members 212a and 212b during the time the recording area of
the recording sheet P between the last toner image T3 and the
trailing edge of the recording sheet is brought close to the
heating members.
[0087] With the above-described modification shown in FIG. 15, more
efficient energy savings can be achieved.
[0088] Next, another image forming apparatus 300 according to the
embodiment of the present invention is explained with reference to
FIGS. 16-18. As shown in FIG. 16, the image forming apparatus 300
is similar to that of FIG. 1, except for a fixing unit 311 and a
power controller 320. The fixing unit 311 is, as shown in FIG. 17,
similar to the fixing unit 11 of FIG. 2, except for a heater 312
that includes heating member 312a-312d for heating the toner image
T. The power controller 320 is shown in FIG. 18 and is similar to
the power controller 20 of FIG. 3, except for a fixing power
control circuit 323. The fixing power control circuit 323 has
separate connections to the heating members 312a-312d, as shown in
FIG. 18, and generates the heater driving signals for driving the
heating members 312a-312d, respectively, in accordance with the
corresponding image information sent from the control unit 22.
Thereby, the heating members 312a-312d of the heater 312 are heated
up and performs the fixing process in accordance with the
corresponding toner images deposited on the recording sheet P. The
above-mentioned heater driving signals are composed of a plurality
of pulses and are hereinafter expressed as the pulse integrate wave
signals A.sub.int-a-A.sub.int-d, as is the case explained with
reference to FIGS. 5A-5C.
[0089] It is noted that the above-described control unit 22 may
either be separated from or unified with the power controller
320.
[0090] Each of the heating member 312a-312d of the heater 312 is a
thermal head or a heater, for example, having a line shape, and
heats the toner image T. The heating member 312a-312d are arranged
in line in the heater 312. The heater 312 is arranged at a position
so that the heating members 312a-312d are orthogonal relative to
the sheet transfer direction. The heating members 312a-312d are
selectively driven by the fixing power control circuit 323 of the
power controller 320 such that the heating members 312a-312d are
not driven at the same time.
[0091] In the above-described fixing unit 311, the toner image T on
the recording sheet P is heated by the heating members 312a-312d of
the heater 312 via the endless belt 13 when the recording sheet P
is fed into the gap between the endless belts 13 and 14. After
that, the recording sheet P is subjected to a cooling process by
which the toner image T is firmly fixed to the recording sheet P
and is then separated from the endless belt 14. At least one of the
guide rollers 16 and 18, arranged downstream from the heater 312 in
the sheet transfer direction, is made of metal having a relatively
high thermal conductivity and serves as a driving roller and a
cooling roller, as is the case with the fixing unit 11 of FIG. 2.
After a completion of the heat fixing process, the toner image T,
the recording sheet P, and the endless belt 13 are cooled by the
guide rollers 16 and 18. The recording sheet P is made close
contact with the endless belts 13 and 14 while it is held by these
endless belts 13 and 14. That is, the toner image T deposited on
the recording sheet P is sealed by the endless belt 13 during the
time the recording sheet P is processed by the fixing unit 311. The
toner image T is therefore not removed from the recording sheet P
when heated. And, the recording sheet P is separated from the
endless belt 13 after the toner image T is sufficiently cooled and
fixed on the recording sheet P so that the toner image T is not
left deposited on the endless belt 13. Thus, the fixing unit 311
outputs an image in a stable quality without causing the
offset.
[0092] In the fixing unit 311, the heater 312 may include any
number of the heating members in place of the heating members
312a-312d.
[0093] FIG. 19 illustrates an alternative structure of the fixing
unit 311. In this structure, a pressure roller 335 that serves as a
pressure roller and a driving roller contacts an endless belt 333
under pressure to form a nip therebetween and drives the endless
belt 333 with friction so that the endless belt 333 rotates in a
direction indicated by an arrow. Therefore, when the recording
sheet P is fed into the gap between the endless belt 333 and the
pressure roller 335, the pressure roller 335 presses the recording
sheet P against a heater 332 via the endless belt 333, wherein the
heater 332 has a plurality of heating members as in the case shown
in FIG. 18. In this structure, the toner image T and the recording
sheet P are cooled by themselves, as indicated by an arrow C, after
a completion of the heat fixing process.
[0094] FIG. 20 expresses a way how the energy of the electric power
for the fixing process is saved when the recording sheet P having
toner images T1-T5, for example, is processed by the fixing unit
311. In this case, the toner images T1-T5 are different in size
from each other, as shown in FIG. 20. During the time the recording
sheet P is present and processed in the fixing unit 311, the
signals A.sub.int-a-A.sub.int-d are held at a low so as to keep the
heating members 312a-312d unheated when no toner image is brought
close to the heating members 312a-312d. When toner image T1 is
brought close to the heater 312, the signal A.sub.int-d is raised
to a high to drive the corresponding heating member 312d. Thereby,
the toner image T1 is heated and fixed on the recording sheet. The
signal A.sub.int-d is then fallen to a low so as to deactivate the
heating member 312d when the toner image T1 is brought away from
the heating member 312d as the recording sheet P is being
transferred in the fixing unit 311. During this operation, the
signals A.sub.int-a-A.sub.int-c are not activated. Therefore, the
fixing process for the toner image T1 is executed with a one-fourth
the power consumption of a case in which a heating member having a
width covering the whole sheet width is activated.
[0095] When toner image T2 is brought close to the heater 312, the
signals A.sub.int-c and A.sub.int-d are raised to a high to drive
the corresponding heating members 312c and 312d. Thereby, the toner
image T2 is heated and fixed on the recording sheet P. The signals
A.sub.int-c and A.sub.int-d are then fallen to a low so as to
deactivate the heating members 312c and 312d when the toner image
T2 is brought away from the heating members 312c and 312d as the
recording sheet P is being transferred in the fixing unit 311. The
remaining signals A.sub.int-a and A.sub.int-b are not activated
during the above-described operation. Therefore, the fixing process
for the toner image T2 is executed with one-half the power
consumption of a case in which a heating member having a width
covering the whole sheet width is activated.
[0096] When toner image T3 is brought close to the heater 312, the
signals A.sub.int-b and A.sub.int-c are raised to a high to drive
the corresponding heating members 312b and 312c. Thereby, the toner
image T3 is heated and fixed on the recording sheet P. The signals
A.sub.int-b and A.sub.int-c are then fallen to a low so as to
deactivate the heating members 312b and 312c when the toner image
T3 is brought away from the heating members 312b and 312c as the
recording sheet P is being transferred in the fixing unit 311. The
remaining signals A.sub.int-a and A.sub.int-d are not activated
during the above operation. Therefore, the fixing process for the
toner image T3 is executed with one-half the power consumption of a
case in which a heating member having a width covering the whole
sheet width is activated.
[0097] When toner image T4 is brought close to the heater 312, the
signals A.sub.int-b, A.sub.int-c, and A.sub.int-d are raised to a
high to drive the corresponding heating members 312b, 312c, and
312d and thereby the toner image T4 is heated and fixed on the
recording sheet P. The signals A.sub.int-b, A.sub.int-c, and
A.sub.int-d are then fallen to a low so as to deactivate the
heating members 312b, 312c, and 312d when the toner image T3 is
brought away from the heating members 312b, 312c, and 312d as the
recording sheet P is being transferred through the fixing unit 311.
During this operation, the remaining signal A.sub.int-a is not
activated. Therefore, the fixing process for the toner image T4 is
executed with three-fourth the power consumption of a case in which
a heating member having a width covering the whole sheet width is
activated.
[0098] When toner image T5 is brought close to the heater 312, the
signals A.sub.int-a, A.sub.int-b, A.sub.int-c, and A.sub.int-d are
raised to a high to drive the corresponding heating members 312a,
312b, 312c, and 312d. Thereby, the toner image T5 is heated and
fixed on the recording sheet P. The signals A.sub.int-a,
A.sub.int-b, A.sub.int-c, and A.sub.int-d are then fallen to a low
so as to deactivate the heating members 312a, 312b, 312c, and 312d
when the toner image T4 is brought away from the heating members
312a, 312b, 312c, and 312d as the recording sheet P is being
transferred in the fixing unit 311. During this operation, all the
signals A.sub.int-a-A.sub.int-d are activated. Therefore, the
fixing process for the toner image T5 is executed with full the
power consumption of a case in which a heating member having a
width covering the whole sheet width is activated.
[0099] During the above-described operations, the signals
A.sub.int-a through to A.sub.int-d are not activated and the
heating members 312a through to 312d of the heater 312 are not
heated when a recording region having no toner image in the
recording sheet P is brought to be passing by the heater 312.
[0100] Thus, the fixing unit 311 can greatly save the energy of
electric power through its fixing operation, as described above.
This would be readily understood by comparing it with a case where
the heating members 312a-212d of the heater 312 are always driven
with continuous driving signals. For example, a text image that has
lines of characters typically includes spaces between the lines.
When such an image is processed by the fixing unit 311, the signals
A.sub.int-a-A.sub.int-d are held at a low at which no energy is
consumed during the time periods corresponding to these spaces.
Thus, a great amount of electric power can be saved.
[0101] FIG. 21 shows a modification of the fixing power control
performed by the fixing power control unit 323. As in the case of
the fixing power control unit 23 of FIG. 3, each of the signals
A.sub.int-a though to A.sub.int-d has three levels; a zero level, a
white level, and a black level. The black level is a level in which
a heating member of the heater 312 is driven in a full power. The
white level is a level in which a heating member of the heater 312
is primarily heated with an electric power with a reduction of 5%
or more from the power of the black level.
[0102] In this case, the toner images T1-T5 are different in size
from each other, as shown in FIG. 21, as in the case of FIG. 20.
During the time the recording sheet P is not present in the fixing
unit 311, the signals A.sub.int-a-A.sub.int-d are held at the zero
level. Also, during the time a non-recording area of the recording
sheet P is brought to be passing by the heater 312, the signals
A.sub.int-a-A.sub.int-d are held at the zero level. When the
recording sheet P is present in the fixing unit 311 and a recording
area of the recording sheet P is brought to be passing by the
heater 312, the signals A.sub.int-a-A.sub.int-d are held at the
white level.
[0103] When toner image T1 is brought close to the heater 312, the
signal A.sub.int-d is raised from the white level to the black
level to drive the corresponding heating member 312d. The toner
image T1 is thereby heated and fixed on the recording sheet P. The
signal A.sub.int-d is then fallen to the white level so as to
pre-heat the heating member 312d when the toner image T1 is brought
away from the heating member 312d as the recording sheet P is being
transferred through the fixing unit 311. The remaining signals
A.sub.int-a-A.sub.int-c are held at the white level during the
above operation. Therefore, in comparison with the power
consumption of a case in which a heating member having a width
covering the whole sheet width is activated, the fixing process for
the toner image T1 is executed with the following reduced power
consumption P1;
P1=(1/4).times.1+(3/4).times.0.95.
[0104] When toner image T2 is brought close to the heater 312, the
signals A.sub.int-c and A.sub.int-d are raised to the black level
to drive the corresponding heating members 312c and 312d. The toner
image T2 is thereby heated and fixed on the recording sheet P. The
signals A.sub.int-c and A.sub.int-d are then fallen to the white
level so as to pre-heat the heating members 312c and 312d when the
toner image T2 is brought away from the heating members 312c and
312d as the recording sheet P is being transferred in the fixing
unit 311. During this operation, the remaining signals A.sub.int-a
and A.sub.int-o are not activated. Therefore, the fixing process
for the toner image T2 is executed with the following reduced power
consumption P2;
P2=(1/2).times.1+(1/2).times.0.95.
[0105] When toner image T3 is brought close to the heater 312, the
signals A.sub.int-b and A.sub.int-c are raised to the black level
to drive the corresponding heating members 312b and 312c. The toner
image T3 is thereby heated and fixed on the recording sheet P. The
signals A.sub.int-b and A.sub.int-c are then fallen to the white
level so as to pre-heat the heating members 312b and 312c when the
toner image T3 is brought away from the heating members 312b and
312c as the recording sheet P is being transferred in the fixing
unit 311. During this operation, the remaining signals A.sub.int-a
and A.sub.int-d are not activated. Therefore, the fixing process
for the toner image T3 is executed with the following reduced power
consumption P3;
P3=(1/2).times.1+(1/2).times.0.95.
[0106] When toner image T4 is brought close to the heater 312, the
signals A.sub.int-b, A.sub.int-c, and A.sub.int-d are raised to the
black level to drive the corresponding heating members 312b, 312c,
and 312d. Thereby, the toner image T4 is heated and fixed on the
recording sheet P. The signals A.sub.int-b, A.sub.int-c, and
A.sub.int-d are then fallen to the white level so as to pre-heat
the heating member 312b, 312c, and 312d when the toner image T4 is
brought away from the heating members 312b, 312c, and 312d as the
recording sheet P is being transferred in the fixing unit 311. The
remaining signal A.sub.int-a is not activated during the
above-described operation. Therefore, the fixing process for the
toner image T4 is executed with the following reduced power
consumption P4;
P4=(3/4).times.1+(1/4).times.0.95.
[0107] When toner image T5 is brought close to the heater 312, the
signals A.sub.int-a, A.sub.int-b, A.sub.int-c, and A.sub.int-d are
raised to the black level to drive the corresponding heating
members 312a, 312b, 312c, and 312d. Thereby, the toner image T5 is
heated and fixed on the recording sheet P. The signals A.sub.int-a,
A.sub.int-b, A.sub.int-c, and A.sub.int-d are then fallen to the
white level so as to pre-heat the heating member 312a, 312b, 312c,
and 312d when the toner image T4 is brought away from the heater
312 as the recording sheet P is being transferred through the
fixing unit 311. During this operation, all the signals
A.sub.int-a-A.sub.int-d are activated and, in this case, the fixing
process for the toner image T5 is executed with the power
consumption same as that of a case in which a heating member having
a width covering the whole sheet width is activated.
[0108] During the above-described operations, the signals
A.sub.int-a through to A.sub.int-d are not activated and the
heating members 312a through to 312d of the heater 312 are not
heated when a recording region having no toner image in the
recording sheet P is brought to be passing by the heater 312.
[0109] Thus, the fixing unit 311 can greatly save the energy of
electric power through its fixing operation with the
above-described modified fixing power control performed by the
fixing power control unit 323. This would be readily understood by
comparing it with a case where the heating members 312a-212d of the
heater 312 are always driven with continuous driving signals. For
example, a text image that has lines of characters typically
includes spaces between the lines. When such an image is processed
by the fixing unit 311, the signals A.sub.int-a-A.sub.int-d are
held at the white level at which an electric power reduction of 5%
or more can be made during the time periods corresponding to these
spaces. Thus, a great amount of electric power can be saved.
[0110] Obviously, numerous additional modifications and variations
of the present invention are possible in light of the above
teachings. It is therefore to be understood that within the scope
of the appended claims, the present invention may be practiced
otherwise than as specifically described herein.
[0111] This document is based on Japanese patent applications, No.
JPAP2000-249839 filed on Aug. 21, 2000, No. JPAP2000-365159 filed
on Nov. 30, 2000, No. JPAP2000-274850 filed on Sep. 11, 2000, and
No. JPAP2001-163025 filed on May 30, 2001 in the Japanese Patent
Office, the entire contents of which are incorporated by reference
herein.
* * * * *